Image Captures From the Yuma FBV Broadband Force-Balance Vertical Seismometer

David F. Nelson
Brett M. Nordgren
For more information: Brett Nordgren <>

See also: Inyo FBV

This image file is captured from the high gain output of the Yuma force-balance vertical seismograph, located approximately two miles from the Pacific Ocean and 19 miles from downtown Los Angeles. The instrument is mounted on a concrete pier, which rests on shallow bedrock made up of weathered Miocene marine sediments.

The instrument's high-gain output has a sensitivity of approximately 315 V/cm/sec (31,462 V/m/sec) over a frequency range of 50 seconds to 30 Hz. This output clips at a level of 10 Volts, which represents 318μm/sec.

The image below is refreshed every 30 minutes.

High gain channel

469nm/sec/line  WinSDR Y-scale factor = 1  50sec – 12.5sec (0.08Hz)  Clipping level 421μm/sec.

These settings greatly reduce microseisms and cultural noise although they also eliminate higher-frequency local quakes and may mask some phases of teleseisms. However the sensitivity is sufficient to occasionaly display surface waves originating from distant quakes having magnitudes in the high 4's, low 5's. Large quakes will be off screen, although the channel clipping level (10V out) is still 421μm/sec. or 36x this screen height.